The goal of this project is to identify and analyze the cellular functions which are required specifically for meiosis in the yeast, Saccharomyces cerevisiae. In particular, we are focusing on the analysis of the SPO11 gene of yeast which is required for recombination and proper chromosome segregation during meiosis. A general system has been developed to isolate specific genes of yeast for which mutants are available. Using this system, the spo11 gene was physically isolated; this represents the first molecular cloning of a meiosis specific gene from any organism. The DNA sequence of the SPO11 gene has been determined and a candidate polypeptide coding sequence of 398 amino acids has been identified and confirmed by hybrid gene fusions. This sequence predicts a strongly basic amino terminal domain. An in vitro engineered gene disruption has been used to demonstrate that the SPO11 gene is essential for meiosis but is not required for vegetative growth or normal progression through the cell cycle. The cloned SPO11 gene has been shown to be expressed only in meiotic cells. Thus, mutation in a single gene is sufficient to disrupt meiotic differentiation and proper chromosome behavior, giving rise to mostly inviable or grossly aneuploid products. Specifically, the SPO11 gene is required for the assembly of the synaptonemal complex. The SPO11 gene product is being expressed by recombinant DNA methods in E. coli to facilitate its biomedical characterization.